The invention relates to a method and system for protecting a conduit in an annular space around a well casing.
Traditionally, a well is constructed from a telescopic like series of steel tubular well casings, to provide well integrity from itself and from the surrounding rock. These well casings are cemented and/or otherwise fixed within the wellbore by some mechanical means. To allow fluids to enter or leave the wellbore it is normal to install and detonate shaped perforating charges to provide a series of penetrations through the steel conduit, cement, and into the surrounding reservoir of choice. The deployment of the perforating charges frequently requires the charges to be installed in the perforating charge carrier or gun in a spiral configuration. Shot densities of 40 shots per meter are common, and means that the entire cross section and longitudinal section of the well casing is a potential, but relatively random, target. Notwithstanding the many years and cost of researching and developing highly efficient shaped charge perforators, successful and efficient perforation is dependent on two basic factors: shot density and phasing.
In gas wells, shot density is important as it minimises turbulence as well as increasing inflow area.
Phasing increases the effective wellbore radius.
It should also not be overlooked that the single purpose of the shaped charge is to penetrate steel, cement and reservoir rock to a depth significantly beyond filter cake depth and other skin effects.
The use for data gathering, sensing, communication, and command and control of Fibre Optic or Electrical cables or small diameter Hydraulic piping (typically 7 mm or ¼″ diameter stainless steel) is usually managed by mechanically clamping these on production tubulars, which are installed as a continuous production/injection fluid conduit and not considered to be part of the well construction tubulars. These cables and conduits are frequently encapsulated with a hard plastic/nylon coating to provide compression and abrasion resistance.
Production tubulars are generally installed in the well after perforating operations have been carried out and therefore any cable or hydraulic conduit clamped to them are protected from perforation damage.
There is a growing requirement for well and reservoir monitoring purposes to install cables and small diameter pipes behind the well construction casings. So doing exposes these items to potential damage or irrevocable failure caused by the unavoidable impact of perforating charges. Ultimately, it doesn't matter what the shot density or phasing is as it is not possible to guarantee the cable orientation.
Current methods to mitigate damage to cables and other conduits arranged outside a casing when a casing is perforated by explosive charges involve magnetic field disturbance detection and/or detection of sonic reflectance anomalies generated by the conduits and subsequently orienting the explosive charge such it does not hit and damage the conduit.
Examples of magnetic field disturbance detection tools are the Powered Orienting Tool (POWIT) and the Wired Perforating Platform (WPP) that are marketed by Schlumberger.
A tool for detecting sonic reflectance anomalies is the Ultra Sonic Imager Tool (USIT) marketed by Schlumberger. Incorporation of a large diameter (D=˜1.25 cm) braided steel cable in the encapsulation of the conduit aids both forms of detection, while also acting as a bumper to additionally protect the conduit.
Currently available 0°—phased perforating charge guns with charges installed in a straight line can be run with the above mentioned magnetic detection tools and an electric rotating orientation tool. The USIT tool requires a separate detection/logging run before the orientation/perforating run.
Use of low-side perforating systems with preset orientation based on a USIT log to perforate horizontal wellbores has also successfully been applied.
Centralization/decentralization, depending on the detection system used, is absolutely crucial in getting reliable line detection and confidently perforating away from the cables and pipes.
Oriented perforating is significantly more expensive than normal perforating. When considering that it may take at least two separate runs, and 0° phasing means less shots per meter, the cost of oriented perforating, even when ignoring reduced production/injection capabilities, approaches three times the cost of conventional 180°/360° phased perforating. Loss of production from sub optimal phasing, added to the cost of orientation could run into millions of US dollars.
It is common to convert monitoring and/or observation wells into producers or injectors after a period of data gathering, so assuming that there is no desire to lose the data gathering and sensing capabilities in a monitoring well when converted, then the behind casing installation means commitment to oriented perforating and the consequential reduced perforating efficiency.
Thus, there is a need to protect cables and other conduits from perforating damage by deflecting the wave front or jet material generated by shaped perforating charges.
There is also a need to provide a means to perforate through a well casing or co-axial set of well casings without damaging any conduit that may be attached by clamps or other means to the outer surface of at least one of the casings.
Furthermore there is a need to remove the requirement to use oriented perforating equipment and allow the use of fully phased perforating guns.
In addition there is a need to provide a means of deploying and clamping a cable or other conduit that may be integrated with the shaped charge deflector and reeled or unreeled during installation.